title: Biochemical characterization and crystal structure of a GH10 xylanase from termite gut bacteria reveal a novel structural feature and significance of its bacterial Ig-like domain.
abstract: Bacterial Ig-like (Big) domains are commonly distributed in glycoside hydrolases (GH), but their structure and function remains undefined. Xylanase is a GH, and catalyzes the hydrolysis of the internal β-xylosidic linkages of xylan. In this study, we report the molecular cloning, biochemical and biophysical characterization, and crystal structure of a termite gut bacterial xylanase, Xyl-ORF19, which was derived from gut bacteria of a wood-feeding termite (Globitermes brachycerastes). The protein architecture of Xyl-ORF19 reveals that it has two domains, a C-terminal GH10 catalytic domain and an N-terminal Big_2 non-catalytic domain. The catalytic domain folds in an (α/β)8 barrel as most GH10 xylanases do, but it has two extra β-strands. The non-catalytic domain is structurally similar to an immunoglobulin-like domain of intimins. The recombinant enzyme without the non-catalytic domain has fairly low catalytic activity, and is different from the full-length enzyme in kinetic parameters, pH and temperature profiles, which suggests the non-catalytic domain could affect the enzyme biochemical and biophysical properties as well as the role for enzyme localization. This study provides a molecular basis for future efforts in xylanase bioengineering.
authors.affiliation: Department of Biochemistry, Virginia Tech, Blacksburg, Virginia, 24061.
authors.forename: Qian
authors.initials: Q
authors.lastname: Han
authors.forename: Ning
authors.initials: N
authors.lastname: Liu
authors.forename: Howard
authors.initials: H
authors.lastname: Robinson
authors.forename: Lin
authors.initials: L
authors.lastname: Cao
authors.forename: Changli
authors.initials: C
authors.lastname: Qian
authors.forename: Qianfu
authors.initials: Q
authors.lastname: Wang
authors.forename: Lei
authors.initials: L
authors.lastname: Xie
authors.forename: Haizhen
authors.initials: H
authors.lastname: Ding
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.forename: Yongping
authors.initials: Y
authors.lastname: Huang
authors.forename: Jianyong
authors.initials: J
authors.lastname: Li
authors.forename: Zhihua
authors.initials: Z
authors.lastname: Zhou
mesh_terms: D000818:Animals; D001419:Bacteria / Q000201:enzymology* / Q000302:isolation & purification; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D041981:Gastrointestinal Tract / Q000382:microbiology; D020049:Isoptera / Q000382:microbiology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014995:Xylosidases / Q000737:chemistry* / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D004269:DNA, Bacterial; D014995:Xylosidases
keywords: bacterial Ig-like domain; bacterium; crystal structure; glycoside hydrolase; intimin; termite gut; xylanase